Originally Posted by AzulDulceFocus
Swapping out the stock receiver in the Focus would only open a who new can of worms and cause problems as everything in the car is tied to that receiver including Sync, and all the steering wheel audio controls.
Most of this is not entirely true, as long as you don't have the Sony MFT stereo.
Metra offers a dash kit for installing a new stereo and a harness assembly and an interface for the steering wheel controls.
They also offer a SYNC retention harness, but you would want a head unit with a rear AUXILIARY input and you would need to use the OEM USB port in the glove box and the new HU would be set to AUX and probably wouldn't show artist and title info. You couldn't use SYNC to change channels, but I don't think you can now either, and I don't think you could use SYNC to change volume.
Also, you would lose Sirius (I think) unless you also added an aftermarket Sirius or XM tuner.
I think the kit and harness would be over $250, so it won't be cheap, but it is possible.